Interactive input systems that allow users to inject input (eg. digital ink, mouse events etc.) into an application program using an active pointer (eg. a pointer that emits light, sound or other signal), a passive pointer (eg. a finger, cylinder or other suitable object) or other suitable input device such as for example, a mouse or trackball, are known. These interactive input systems include but are not limited to: touch systems comprising touch panels employing analog resistive or machine vision technology to register pointer input such as those disclosed in U.S. Pat. Nos. 5,448,263; 6,141,000; 6,337,681; 6,747,636; 6,803,906; 7,232,986; 7,236,162; and 7,274,356 assigned to SMART Technologies ULC of Calgary, Alberta, Canada, assignee of the subject application, the entire contents of which are incorporated by reference; touch systems comprising touch panels employing electromagnetic, capacitive, acoustic or other technologies to register pointer input; tablet personal computers (PCs); laptop PCs; personal digital assistants (PDAs); and other similar devices.
Above-incorporated U.S. Pat. No. 6,803,906 to Morrison et al. discloses a touch system that employs machine vision to detect pointer interaction with a touch surface on which a computer-generated image is presented. A rectangular bezel or frame surrounds the touch surface and supports imaging devices in the form of digital cameras at its corners. The digital cameras have overlapping fields of view that encompass and look generally across the touch surface. The digital cameras acquire images looking across the touch surface from different vantages and generate image data. Image data acquired by the digital cameras is processed by on-board digital signal processors to determine if a pointer exists in the captured image data. When it is determined that a pointer exists in the captured image data, the digital signal processors convey pointer characteristic data to a master controller, which in turn processes the pointer characteristic data to determine the location of the pointer in (x,y) coordinates relative to the touch surface using triangulation. The pointer coordinates are conveyed to a computer executing one or more application programs. The computer uses the pointer coordinates to update the computer-generated image that is presented on the touch surface. Pointer contacts on the touch surface can therefore be recorded as writing or drawing or used to control execution of application programs executed by the computer.
Multi-touch interactive input systems that receive and process input from multiple pointers using machine vision are also known. One such type of multi-touch interactive input system exploits the well-known optical phenomenon of frustrated total internal reflection (FTIR). According to the general principles of FTIR, the total internal reflection (TIR) of light traveling through an optical waveguide is frustrated when an object such as a pointer touches the optical waveguide surface, causing some light to escape from the touch point. In a multi-touch interactive input system, the machine vision system captures images including the point(s) of escaped light, and processes the images to identify the position of the pointers on the optical waveguide surface based on the point(s) of escaped light for use as input to application programs.
One example of an FTIR multi-touch interactive input system is disclosed in U.S. Patent Application Publication No. 2008/0029691 to Han. Han discloses an optical waveguide in the form of a clear acrylic sheet, directly against a side of which multiple high-power infrared light emitting diodes (LEDs) are placed. The infrared light emitted by the LEDs into the acrylic sheet is trapped between the upper and lower surfaces of the acrylic sheet due to total internal reflection. A diffuser display surface is positioned over the non-contact side of the acrylic sheet with a small gap between the two in order to keep the diffuser display surface from frustrating the total internal reflection. According to one embodiment, a compliant surface overlay is disposed adjacent the contact surface of the acrylic sheet, with another small gap between the two layers in order to prevent the compliant surface overlay from frustrating the total internal reflection unless it has been touched. When touched, the compliant surface overlay in turn touches the acrylic sheet and frustrates the total internal reflection.
As will be appreciated, in interactive input systems that employ imaging devices to acquire images that are processed to detect pointer input, lighting is an important factor. In order for pointer contacts to be quickly and accurately determined while avoiding false pointer contacts, pointers must appear clearly in captured image frames. To facilitate pointer detection, illumination sources are often used with interactive input systems that employ imaging devices. These illumination sources emit radiation that is either occluded by pointers so that pointers appear as dark regions in an otherwise light image frame, or reflected by the pointers so that pointers appear as light regions in an otherwise dark image frame.
For example, U.S. Pat. No. 6,972,401 to Akitt et al. issued on Dec. 6, 2005 and assigned to SMART Technologies ULC, discloses an illuminated bezel for use in a touch system such as that described in above-incorporated U.S. Pat. No. 6,803,906. The illuminated bezel emits infrared or other suitable radiation over the touch surface that is visible to the digital cameras. As a result, in the absence of a passive pointer in the fields of view of the digital cameras, the illuminated bezel appears in captured images as a continuous bright or “white” band. When a passive pointer is brought into the fields of view of the digital cameras, the passive pointer occludes emitted radiation and appears as a dark region interrupting the bright or “white” band in captured images allowing the existence of the pointer in the captured images to be readily determined and its position determined using triangulation.
In interactive input systems that employ illumination sources, ideally only illumination emitted by the illumination sources is detected by the imaging devices during image frame capture so that any pointer in the captured image frame can be clearly identified. Unfortunately, in most environments, during image frame capture detrimental light such as for example sunlight, light emitted by external sources, glare etc. is also detected by the imaging devices. This detrimental light can have a negative impact on the quality of captured image frames making it more difficult to identify pointers in captured image frames. Improvements are therefore desired.
It is therefore an object of the present invention to provide a novel interactive input system with improved signal-to-noise ratio and a novel image capture method.